Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session H3: Quantum Measurement and Collective Effects |
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Chair: Ivan Deutsch, University of New Mexico Room: A703 |
Wednesday, June 15, 2011 8:00AM - 8:12AM |
H3.00001: BEC in a double-well trap: back-action from measurements of atom numbers forces classical behavior Juha Javanainen, Yi Li We consider a double-well trap containing a BEC, assuming that the numbers of the atoms on both sides of the trap are monitored continuously using light scattering. A master equation giving the exact quantum evolution is solved by means of quantum trajectory simulations. In parallel, we develop a corresponding classical model, a variation of mean-field theory, by expanding the equation of motion of the Wigner function as a power series in the inverse of the atom number. In this formulation random diffusion of the relative phase of the condensates in the two wells represents the quantum mechanical back-action of the measurements of the atom numbers. In our numerical examples the quantum and classical descriptions give results so similar that in practice it would be impossible to tell them apart experimentally, even under circumstances when mean-field theory is expected to fail. [Preview Abstract] |
Wednesday, June 15, 2011 8:12AM - 8:24AM |
H3.00002: Spin squeezing in spin-1 Bose condensates Chris Hamley, Corey Gerving, Thai Hoang, Michael Chapman Spin-1 condensates are predicted to generate non-classical states with quantum correlations, specifically spin squeezed states. We investigate these non-classical states experimentally along with a theoretical background to describe them in the single mode approximation. We will report on progress towards observing non-classical states generated by spin mixing using Rb-87 F = 1 condensates confined in optical trap. [Preview Abstract] |
Wednesday, June 15, 2011 8:24AM - 8:36AM |
H3.00003: Backaction-limited measurement, cavity feedback, and ponderomotive squeezing in ultracold atom optomechanics Thierry Botter, Daniel W.C. Brooks, Nathan Brahms, Thomas P. Purdy, Sydney Schreppler, Dan M. Stamper-Kurn A large variety of optomechanical systems have been constructed with the goal of making quantum-limited measurements of mechanical motion. Here we present a cavity optomechanics system where the resonator is composed of a gas of ultracold atoms. The resonator is prepared in its ground state, and can operated in the single-photon strong-coupling regime. Using this system, we obtain measurement sensitivity that is limited by measurement backaction. We additionally observe gain and attenuation of radiation-pressure fluctuations due to cavity-optomechanical feedback, including signatures of ponderomotive squeezing. [Preview Abstract] |
Wednesday, June 15, 2011 8:36AM - 8:48AM |
H3.00004: Quantum Control and Measurement in the 133Cs Full Hyperfine Ground Manifold Brian Anderson, Aaron Smith, Hector Sosa, Poul Jessen, Carlos Riofrio, Ivan Deutsch Quantum systems with Hilbert space dimension greater than two (qudits) are often considered as carriers of quantum information. The use of qudit systems could prove advantageous for information processing tasks, provided that good laboratory tools for robust qubit manipulation and readout can be developed. We have successfully implemented a protocol for arbitrary state mapping in the 16-dimensional hyperfine ground manifold of the Cesium 133 atom, using only DC, rf and microwave magnetic fields and thus avoiding the photon scattering and decoherence characteristic of schemes that rely on optical fields. Our control waveforms are designed to provide robustness against errors and inhomogeneities in the control fields, and this has allowed us to achieve state mapping fidelities of 98\% or better in the laboratory. We have developed a procedure involving successive applications of state mapping waveforms, allowing us to separate qudit initialization and readout errors from state mapping errors, and thus to reliably measure state mapping fidelities in excess of 99\%. [Preview Abstract] |
Wednesday, June 15, 2011 8:48AM - 9:00AM |
H3.00005: Early stage of Superradiance from Bose-Einstein condensates Lukas Buchmann We investigate the dynamics of matter and optical waves at the early stage of superradiant Rayleigh scattering from Bose-Einstein condensates, an instance of four-wave-mixing of matter and optical waves. Our analysis is within a spatially dependent model which treats the matter-waves as well as the optical end-fire modes quantum mechanically and is capable of providing analytic solutions for the operators of interest. In particular, we study the statistical properties of the outgoing scattered light which provide insight into the rich internal dynamics of the system at this early stage. Furthermore, we investigate coherence properties of pairs of counter propagating atomic sidemodes produced during the process. It is shown that these clouds exhibit long-range spatial coherence and strong nonclassical density cross-correlations due to entanglement between the clouds. These findings make this scheme a promising candidate for the production of highly directional nonclassically correlated atomic pulses. Our prediction of number difference squeezing between the clouds was observed in another instance of a four-wave mixing process using metastable helium. [Preview Abstract] |
Wednesday, June 15, 2011 9:00AM - 9:12AM |
H3.00006: Superradiance in spin-J atoms: Effects of multiple atomic levels Guin-Dar Lin, Susanne Yelin We study the superradiance dynamics in a dense system of atoms each of which can be generally a spin-J particle with J an arbitrary half-integer. Using a novel formalism we derive an effective two-body master equation to study the relevant cooperative and collective effects, taking into account the coherence of transitions between different atomic levels. One direct application of such calculation is to study the superradiance, in the context of polar molecules, due to transitions between multiple excitation levels, e.g. vibrational modes. [Preview Abstract] |
Wednesday, June 15, 2011 9:12AM - 9:24AM |
H3.00007: Cavity QED systems with group II atoms and the crossover between lasing and superradiance David Tieri, Dominic Meiser, Murray Holland Recently, cavity QED systems with an optical transition with a decay rate many orders of magnitude smaller than than normal dipole allowed optical transitions have been realized experimentally. These new systems allow access to investigate the crossover between lasing and superradiance. We model such systems theoretically using a master equation, and solve this equation using the quantum state diffusion algorithm. We discuss the statistical properties of the generated light. A solid understanding of this crossover regime could allow us to transplant some of the knowledge and methods from the laser side to the steady steady superradiance side, where we have recently demonstrated the possibility of a mHz linewidth light source. [Preview Abstract] |
Wednesday, June 15, 2011 9:24AM - 9:36AM |
H3.00008: Stochastic light shifts of ground-state quantum beats Andres Cimmarusti, David Norris, Luis Orozco, Pablo Barberis-Blostein, Howard Carmichael We present evidence of light shifts opposite in sign to the AC Stark shift that influence the evolution of atomic ground-state superpositions. We drive $^{85}$Rb atoms, near resonance, with a mode of an optical cavity in the presence of a weak magnetic field and monitor fluctuations in spontaneous emission into an orthogonal mode. Beats appear from a coherent ground-state superposition that evolves in time between photon emissions. Analysis of intensity autocorrelations reveals oscillations at twice the ground-state Larmor frequency. The beats depend on magnetic field magnitude, laser detuning and intensity. We find that small phase shifts coming from successive spontaneous emissions cumulatively and stochastically give rise to frequency shifts, of the order of hundreds of kilohertz per photon, along with dephasing of the superpositions due to the phase diffusion process. [Preview Abstract] |
Wednesday, June 15, 2011 9:36AM - 9:48AM |
H3.00009: Rotary echos for the preservation of quantum memories Hermann Uys, Ludwig De Clerq, Todd Green, Michael Biercuk, John Bollinger Dynamical decoupling is a promising technique for fighting the unwanted effects of decoherence in the context of quantum information. Decoupling techniques span two extremes from pulsed spin-echo sequences to optimized, continuous amplitude and phase modulation allowing arbitrary rotations on the Bloch sphere. On the one hand spin-echo techniques have the advantage of simplicity, while on the other optimized continuous modulation is expected to achieve better performance results at the cost complexity. That complexity exists both in the implementation and the modulation design, which either requires intimate knowledge of the relevant noise environment for numerical optimization or experimental optimization through feedback. Rotary echos represent an intermediate approach which have the advantage of continuous averaging of dephasing noise and pulsed compensation of fluctuations in the control field amplitude. Here we consider a classical dephasing noise environment and compare the performance of rotary echos to both pulsed and optimized continuous control decoupling techniques. [Preview Abstract] |
Wednesday, June 15, 2011 9:48AM - 10:00AM |
H3.00010: Single Ion Quantum Lock-In Amplifier Shlomi Kotler, Nitzan Akerman, Yinnon Glickman, Anna Keselman, Roee Ozeri Invented by Dicke, the lock-in measurement is a phase-sensitive detection scheme that can extract a signal with a known carrier frequency from an extremely noisy environment. Here we report on the implementation of a quantum analog to the classical lock- in amplifier. All the lock-in operations: modulation, detection and mixing, are performed via the application of non-commuting quantum operators on the electronic spin state of a single trapped Sr+ ion. We increase its sensitivity to external fields while extending phase coherence by three orders of magnitude, to more than one second. With this technique we measure magnetic fields with sensitivity of $25\ pT/\sqrt{Hz}$, and light shifts with an uncertainty below $140\ mHz$ after $1320$ seconds of averaging. These sensitivities are limited by quantum projection noise and, to our knowledge, are more than two orders of magnitude better than with other single-spin probe technologies. As a first application we perform light shift spectroscopy of a narrow optical quadruple transition. We remark that the quantum lock-in technique is generic and can potentially enhance the sensitivity of any quantum sensor. (http://arxiv.org/abs/1101.4885) [Preview Abstract] |
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